Mechanical parking meters were originally developed for insertion of coins or tokens through a coin slot into a coin chute that would facilitate gauging the size of the coins before dropping them into a coin box. Based on the size of the coin, the appropriate time would be wound onto the meter and displayed with a pointer and dial. This method required inserting the coins into their proper slots and turning a handle. Mechanical meters could not distinguish a valid coin from an object the size of a valid coin. Also, this method was prone to jamming and would require partial disassembly of the meter to repair the jams.
Electronic meters were later developed with free-fall coin shoots with electronic methods of gauging coins and with straight fall into the coin box that would make jams less frequent and easier to clear. However, this design gave way to a new method of cheating the parking meters by controlling and retrieving the coin or token with a string, such as an ordinary string or fishing line, ribbon, plastic straw, or other attachments. The “coin-on-a-string” trick allowed the coin to be recovered after purchasing time and/or could be used to purchase multiple increments of time thereafter.
A mechanical “catch” inside the coin shoot has been employed to stop retrieval of a coin or token, but when the catch forced upward, the catch may cause jams in the coin shoot, may break off completely or otherwise render the parking meter inoperable. Additionally, a rigid attachment of the coin, such as to a flat piece of plastic or a flattened drinking straw, can actually flatten the catch against the wall of the coin shoot and holding down the catch while the coin passes over and is then retrieved.
For this reason, a need exists for an improved system and method for detecting fraudulent control of coins inserted into vending machines, such as parking meters, that overcomes the shortcomings of prior systems.